1. Field of the Invention
This invention relates to a signal line system, and more particularly to a signal line system used in a semiconductor memory or the like in which crosstalk between signal lines can be effectively prevented.
2. Description of the Prior Art
Semiconductor production techniques have shown remarkable progress in recent years, and various elements which constitute semiconductor integrated circuits are becoming smaller in size. As a result of this technological progress, integrated circuits are mounted on a semiconductor substrate with a greater density and with a greater functionality. This has also narrowed the distance between signal lines disposed on the substrates.
Particularly in the case of dynamic semiconductor memory devices, the crosstalk between signal lines which transfer very-low level signals output from memory cells to sense amplifiers greatly effects the reliability of the product as the integrating density increases. Therefore, signal line systems having a configuration for preventing the crosstalk have been proposed.
FIG. 3 shows one example of such conventional signal line systems ("A Memory Array Architecture for 16 Mb DRAMs", M. Tsukude et al., SDM89-31, 1989). The system shown in FIG. 3 comprises four pairs of signal lines (bit lines) which connect memory cells (not shown) with sense amplifiers S1-S4, respectively. More specifically, the first pair (signal lines B1 and B#1) is connected to the sense amplifier S1, the second pair (signal lines B2 and B#2) to the sense amplifier S2, the third pair (signal lines B3 and B#3) to the sense amplifier S3, and the fourth pair (signal lines B4 and B#4) to the sense amplifier S4. In each of the signal line pairs B1 and B#1, B2 and B#2, B3 and B#3, the two signal lines are arranged so that they cross each other and so that the crossing of one signal line pair opposes the straight part of another signal line pair.
In such a signal line system of the prior art, even if signals passing through the signal lines B2 and B#2 are induced as a crosstalk signal on the signal line B1 which is disposed adjacent to both the signal lines B2 and B#2, the signals on the signal lines B2 and B#2 are opposite in phase. Therefore, the crosstalk signals induced on the signal line B1 are also opposite in phase, which causes them to cancel each other. A similar kind of crosstalk cancellation effect is obtained between adjacent signal line pairs. That is, the crosstalk induced by each of the signal line pairs can be reduced by the crossings in the signal line pairs.
In a signal line system of the prior art having such a configuration, the crosstalk between adjacent signal line pairs can be reduced, while the crosstalk between signal lines of the same pair (i.e., between the respective signal lines B1 and B#1, B2 and B#2, B3 and B#3, and B4 and B#4) which are connected to the respective sense amplifiers S1 to S4 cannot be reduced. Furthermore, since the signals output from the same memory cell to the corresponding one of the sense amplifiers S1 to S4 are always opposite to each other in phase, this kind of crosstalk further attenuates the signal level, which reduces the margin of each of the sense amplifiers S1 to S4.